Method of making an electrical device comprising a glass capsule and a wire lead fused therein



Dec. 7, 1965 P. c. DEMAREST 3,221,386

METHOD OF MAKING AN ELECTRICAL DEVICE COMPRISING A GLASS CAPSULE AND A WIRE LEAD FUSED THEREIN Filed July 7. 1960 Fig.1

al/ V IN V EN TOR.

P/Zila'p C. Berna/"est United States Patent 3,221,386 METHOD OF MAKING AN ELECTRICAL DEVICE COMPRISING A GLASS CAPSULE AND A WIRE LEAD FUSED THEREIN Phili C. Demarest, Pine Brook, N..l., assignor to Ohmega Laboratories, Pine Brook, N..I., a corporation of New Jersey Filed July 7, 1969, Ser. No. 41,417 7 Claims. (Cl. 29--25.11)

This invention relates to an encapsulated electrical device and to the glass capsule therefor and to the method by which the device and glass capsule are made.

One of the most important trends in modern electronic devices is toward a reduction of size of the various components. In some instances, such as in devices to be carried by airplanes, rockets, or missiles, a reduction of size is a necessity because of the limited space and weightcarrying capacity available, but even in electronic device and systems for earthbound use, the trend toward extreme miniaturization, frequently referred to as microminiaturization, opens up whole vistas of uses not previously considered.

More specifically, there has been a continuing effort to reduce the size of electric lights. This has been carried to the point of making electric lights as small as a grain of wheat, but technology available prior to the present invention did not permit a reduction of size much below that point.

It is one of the primary objects of the present invention to form a glass bulb, or capsule, smaller than has hitherto been available for encapsulating electrical devices, such as electric lights and the like.

Another object is to provide an improved method for assembling and sealing microminiature electrical devices including electric lights.

Furthcr objects will appear from the following specification, together with the drawings in which:

FIG. 1 shows certain of the components at one stage of the process of making a glass capsule according to the invention;

FIG. 2 shows an assemblage of the components at a later stage in the process of making a capsule and electrical device according to the invention;

FIG. 3 shows additional parts at a succeeding stage in the process; and

FIG. 4 shows a cross-sectional view of an electric lamp formed according to the process of the invention and as an outcome of the process, the steps of which are depicted in FIGS. 1 through 3.

In accordance with the invention, the capsule, or bulb, of a microminiature electrical device, such as an electric light, is formed by taking a minute, hollow, glass tube, cutting off a portion of it and threading it over the bight of a slender wire that has been doubled back on itself. A suitable voltage is applied to the ends of the Wire to drive an electric current therethrough to heat the wire up sufliciently to melt the short piece of glass tubing and cause it to coalesce into a ball which is attached to the wire. An electrical component, such as one end of an electric lamp filament, is attached to the bight of the wire to which the glass has been scaled, and the electrical component, together with the bight end of the wire is inserted into the end of the minute glass tube. Thereupon, the wire is again connected to a source of electric current which again produces enough heat in the wire to remelt the glass ball and the contiguous part of the glass tube so that the glass of the ball and the tube flow together to make a single hermetic junction. Thereafter the ends of the wire may serve as electrical terminals for the component within the glass tube.

ice

While the wire has been spoken of as being doubled on itself, the essential requirement is that both ends of the wire be available for connection to a source of electric current in order that the wire may be heated sufficiently to melt the glass. The exact shape of the wire is secondary to this requirement.

Referring to FIG. 1 in which the first step of the formation of an electric light bulb is shown, a simple U- shaped form of wire 11 is indicated. The bight end of this wire is inserted through a short length of hollow glass tubing 12 and the ends of the wire are connected to a battery 13 indicated as being variable so as to control the heat produced by the wire. As a reuslt of this heat the glass tubing 12 melts, beginning with that portion which is contiguous with the wire 11 but eventually including all of the glass in this short length of tubing. As a result of the force of surface tension, the mass of glass coalesces into a solid ball attached to the wire.

Preferably, a refractory metal, such as platinum, is used for the wire 11 since it must be a metal that can be heated to the necessary high temperatures without unduly oxidizing. The glass material of which the tubing 12 is formed preferably has a coeflicient of thermal expansion equal or approximately equal to that of the metal of the wire 11. In the case of platinum, a lead glass having a coeificient of expansion about 9() 10 units/ unit length/degree centigrade is used. Lead glass also has the advantages of being a very good electrical insulator and of melting at a relatively low temperature sufficiently to permit surface tension to cause the tubing 12 to assume a substantially spherical shape.

FIG. 2 shows the components of an electric light using two of the assemblages formed according to the process just described in connection with FIG. 1. The left-hand assemblage consists of the wire 11, glass ball 14 which is the shape assumed by the short glass rod 12 of FIG.1 under the force of surface tension after the glass has been heated to the molten state. A similar assemblage on the right consists of wire 16 similar to the wire 11 and a glass bulb 17 hermetically sealed to the wire 16. An electrical component, in this case a filament 18 capable of incandescing, extends from the bight 19 of the wire 11 to that of the wire 16, identified by reference character 20. The filament 18 is hooked into each of the bights 19 and 20, after which the portions of the wires 11 and 16 that form their respective bights are pressed into place by mechanical force to grip the ends of the filament 18 in order to maintain good electrical contact therewith. A hollow glass tubing 21 is fitted over the filament 18 and over the two glass balls 14 and 17. The glass of which the tubing 21 is made must have characteristics that will permit it to seal to the glass of the balls 14 and 17. This is most easily realized by using the same type of glass for both the balls 14 and 17 and the tubing 21, although in certain circumstances it may be desirable to use a different type of glass material for the tubing 21. In fact, not only may the same type of glass be used, but the balls 14 and 17 may be formed from tubing of the same size as the tubing 21. Illustrative of how small the diameter of this tubing may be is the fact that lamps can be made commercially having a diameter of only .015, far smaller than has heretofore been possible.

FIG. 3 shows a succeeding step in the process of manufacturing a light bulb according to the invention. In order for the ends of the tubing 21 to seal to the glass balls 14 and 17, sufficient heat must be transferred, first from the wires 11 and 16 to the balls 14 and 17, and thence to the tubing 21. For this purpose it is preferable to make the diameter of the balls 14 and 17 substantially equal to the inner diameter of the glass tubing 21. By controlling the length of the tubing 12 shown in FIG. 1, the

diameter of the glass ball formed therefrom can be con trolled very closely, for example to within .001". In order to assure a more definite physical contact between the glass balls and the inner wall of the tubing 21, a heated rod or wire may be touched to the end of the tubing 21 to raise its temperature above the melting point slightly and thereby tack it to the ball 14, as shown. The other end of the tubing 21 may be similarly tacked to the ball 17.

The final stage in the process of manufacture of an electric light bulb according to the invention is to place the assembly of FIG. 3 into an evacuated chamber and to connect the ends of the wires 11 and 16 respectively to suitable voltage sources. These sources are indicated in FIG. 4 by reference characters 13 and 22, source 13 being the same as that in FIG. 1 and being again connected to the ends of the wire 11 and source 22 being connected to the ends of the Wire 16. Both of these sources are variable so as to control the amount of heat generated in the wires 11 and 16 by the electrical current.

As indicated in FIG. 4, when sufficient heat is generated in the wires 11 and 16, the balls 14 and 17 are again raised to the temperature at which they melt, except that this time they are in contact with the glass tubing 21, the ends of which also melt and mingle with the glass of the balls 14 and 17, forming a monolithic mass at each end of the bulb. The bulb so formed may be quite small, of the order of .062" for commercial light bulbs, for example.

In order for the light bulb to have a long life, it is necessary to drive as much air and water vapor as possible out of the bulb while it is being warmed. Of course, the very fact that the bulb is placed in an evacuated space during the sealing-off process is suflicient in itself to withdraw most of the air and other deleterious substances, but in order to assist this evolution process further, a source of voltage 23 is connected between the wires 11 and 16 and in series with the filament 18 to cause the latter to heat up during the sealing process of the bulb. This not only drives off gas absorbed on the face of the filament itself, but also gas on adjacent portions of the inner surface of the tubing 21.

FIG. 4, in addition to showing the final configuration of the glass capsule of the light bulb, also shows a modified arrangement :for holding the ends of the filament 18. In FIG. 4, the ends of the bights 19 and 20 are folded back on top of the ends of the filament 18 and are pressed into place mechanically to grip the ends of the filament.

While this invention has been described in terms of specific embodiments, it will be recognized by those skilled in the art that neither the item itself nor the method of making it are limited to the precise forms described, but

:that the true scope of the invention is defined by the following claims.

What is claimed is:

1. The process of sealing a capsule comprising the steps of: threading a Wire lead through a hollow glass bead; heating said bead only by passing an electric current through said wire to melt said head into a coherent mass attached to said wire; inserting said mass into one end of a hollow glass tube; and heating said mass and the contiguous part of said tube to the temperature at which they melt and flow together only by passing electric current through said wire.

2. The process of sealing a capsule comprising the steps of forming a wire lead into a U-Shape; threading a hollow glass head over the bight of said wire; heating said bead only by passing an electric current through said W re o melt said bea into a coherent mass hermetically sealed to said wire; inserting said coherent mass and the bight of said wire into one end of a hollow glass tube; and heating said mass and the contiguous part of said tube to the temperature at Which they melt and flow together only by passing electric current through said wire.

3. In the process of manufacturing an electric lamp the steps comprising: forming a wire into a U-shape; threading a hollow glass bead over the bight of said wire; heating said bead only by passing an electric current through said wire to melt said bead into a coherent mass hermetically sealed to said wire; attaching one end of a fine wire filament to the bight of said first-named wire; inserting said filament and the bight of said first-named wire and said mass of glass into one end of a hollow glass tube; and heating said mass and the contiguous part of said tube to the temperature at which they melt and flow together only by passing electric current into said wire.

4. The process of claim 3 in which the bight of said first-named wire is folded back upon itself to clamp one end of said filament and to make firm electrical and mechanical contact therewith.

5. The process of claim 3 in which both ends of said first-named wire are kept outside of said glass tube.

6. The process of forming an electric lamp comprising the steps of forming a first wire lead into a U-shape; forming a second wire lead into a U-shape; threading hollow glass beads over the bights of each of said wire leads, respectively, heating said beads only by passing electric current through each of said wire leads to melt said beads into coherent masses hermetically sealed to said wire leads; attaching one end of a fine Wire filament to one of said bights and the other end of said filament to the other of said bights; placing a hollow glass tube over said fila ment and over both of said bights and over both of said coherent masses; placing the structure thus formed in a vacuum chamber; and heating each of said masses and the contiguous parts of said tube to the temperature at which each of said masses and each of said contiguous parts melts and flows together, respectively, only by passing separate electric current through each of said wire leads.

7. The process of claim 6 including the additional step of passing a separate electric current from one end of one of said wire leads through said filament to one end of the other of said wire leads to heat said filament simultaneously with the step of heating said coherent masses and the contiguous parts of said glass tubing.

References Cited by the Examiner UNITED STATES PATENTS 241,464 1/1881 Beeman 313-274 253,647 2/ 1882 Voelker 2925.15 266,447 10/ 1882 Edison 29-25 .11 282,472 7/1883 Swan 6540 370,999 10/ 1887 Thompson 2925. 11 532,760 1/1895 Branin 2925.15 X 1,028,118 6/1912 Knowles 313274 1,564,690 12/1925 Kruh et al. 2925.11 2,191,346 2/1940 Greiner 313-274 2,324,557 7/ 1943 Claesson 2925.15 X 2,791,480 5/1957 Larson 316--19 2,992,874 7/ 1961 Germeshausen 31619 3,040,204 6/1962 Belknap 2925.13 3,069,583 12/ 1962 Swasey 2925 .13

RICHARD H. EANES, JR., Primary Examiner. ARTHUR GAUSS, LEON PEAR, Examiners. 

1. THE PROCESS OF SEALING A CAPSULE COMPRISING THE STEPS OF: THREADING A WIRE LEAD THROUGH A HOLLOW GLASS BEAD; HEATING SAID BEAD ONLY BY PASSING AN ELECTRIC CURRENT THROUGH SAID WIRE TO MELT SAID BEAD INTO A COHERENT MASS ATTACHED TO SAID WIRE; INSERTING SAID MASS INTO ONE END OF A HOLLOW GLASS TUBE; AND HEATING SAID MASS AND THE CONTIGUOUS PART OF SAID TUBE TO THE TEMPERATURE AT WHICH THEY MELT AND FLOW TOGETHER ONLY BY PASSING ELECTRIC CURRENT THROUGH SAID WIRE. 